A transceiver is a device, containing a transmitter and a receiver, which is thus capable of transmitting and receiving communication signals, respectively. Conventionally, the transmitter contains a power amplifier (PA) that provides the last stage of amplification of the signal to be transmitted.
In some conventional designs, the power amplifier is implemented as a component that is physically separate from other parts of the transmitter and/or transceiver. Also, power amplifiers made from gallium arsenide (GaAs) or silicon bipolar junction transistors (SiBJT) are typically used because they have an inherently higher breakdown voltage than transistors made in a CMOS circuit, whether the transistors are n-channel or p-channel transistors. While such designs allow for a power amplifier that has the desired amplification characteristics, they do so at the expense of cost. Not only is a GaAs, SiBJT or other non-CMOS power amplifier transistor costlier than a transistor in a CMOS integrated circuit, but the non-CMOS power amplifier cannot be formed on the same integrated circuit chip as the components of the transmitter and/or transceiver. Both of these factors add to the overall cost of the resulting transceiver.
It has been recognized that it would be beneficial to have a transceiver in which most of the transmitter and receiver circuits are on a single chip, including the power amplifier. For example, in the article entitled A Single Chip CMOS Direct-Conversion Transceiver for 900 MHz Spread Spectrum Digital Cordless Phones by T. Cho et al. that was presented at the 1999 IEEE International Solid State Circuits Conference, there is described a CMOS transceiver chip that includes an integrated power amplifier. An improved CMOS power amplifier is also described in the application entitled CMOS TRANSCEIVER HAVING AN INTEGRATED POWER AMPLIFIER, bearing application Ser. No. 09/663,101, filed on Sep. 15, 2000 and assigned to the same assignee as the assignee of the invention described herein, which recognizes the advantage of integrating the power amplifier.
Nevertheless, some CMOS power amplifiers exhibit power level variation due to their sensitivity to thermal and process variations. These sensitivities may limit the accuracy of conventional means of providing variable gain in a CMOS power amplifier. High efficiency and constant power levels in CMOS power amplifiers may be impeded by low breakdown voltage, low current drive, and lossy substrate.
Accordingly, an improved gain control technique for transceivers would be useful.